What does it means the "!" suffix in a method?

[Skyblaze]

I'm reading the sitepoint's rails book and i don't understand if the "!" suffix to method names is optional for all built-in methods (for example i use it whenever i want that method operates on the object directly in a destructive manner instead of operates on a copy of it) or it is optional only for methods that supports it.

[vgarcia]

Only for methods that support it, not for all methods. For example, if you look at the documentation for the Array class, you'll see map() and map!(), but no sort!() method to go along with sort().

[Skyblaze]

ok as i imagined

[Fenrir2]

There *is* a sort! method. I don't know why it isn't documented.

There is no magic in the ! suffix: it's just an extra character allowed in Ruby method names. sort and sort! are two technically unrelated methods. They could be called sort and destructive_sort, but Ruby uses the ! *convention*. Many built in methods have a related destructive method.

class Array
  def sort
    ...
  end

  def sort!
    ...
  end
end

You can find these using:

[].methods.grep /!/

Which gives us all ! methods supported by Array:

["collect!", "compact!", "reject!", "slice!", "map!", "flatten!", "reverse!", "uniq!", "sort!"]